Bubble-Liquid Membrane Method for Preparing Spherical Calcium Carbonate Nanoparticles

In this work, we describe the principle and operation of a bubble-liquid membrane reactor, and use of the reactor to prepare spherical calcium carbonate nanoparticles. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and laser particle size analysis. The effects of additives to control crystal morphology, coating agents, and the stirring speed of the bubble-liquid membrane reactor were investigated. Spherical calcium carbonate nanoparticles with uniform dispersion and no agglomeration were obtained when a disodium hydrogen phosphate/ethylenediaminetetraacetic acid disodium salt mixture (1:1 mass ratio) was used as the additive, oleic acid was used as the coating agent (1.5 wt%), and the stirring speed was 5000–6000 r/min. The results indicate that the bubble-liquid membrane reactor may be suitable for continuous industrial production of calcium carbonate nanoparticles.

Maleic Rosin-based Gemini Surfactant as Air Entraining Agent for Concrete under Low Air Pressure

The effectiveness of Air entraining agent (AEA) in concrete under low air pressure in the plateau area decreased. A type of new AEA, named MRE was synthesized to increase bubbles` stability in fresh concrete under low air pressure. The performance of MRE solution and concrete with MRE were tested under 60 kPa and 100 kPa compared with commercially gemini AEA (DCC). The test results showed that the foam volume of MRE and DCC solution under 60 kPa was reduced by 3% and 9% than under 100 kPa. The bubble liquid film strength of MRE is 63% higher than that of DCC. For concrete with MRE and DCC under 60 kPa, the air content was 2% and 16% lower, the relative dynamic modulus of concrete reduced by 6% and 15%, and the bubble spacing factor under 60 kPa increased by 17% and 39% respectively compared with that under 100 kPa. MRE can increase the freeze-thaw resistance of concrete under low air pressure without affecting concrete strength and is suitable for high altitude concrete.

Enhancing Ion Flotation through Decoupling the Overflow Gas and Liquid Fluxes

Conventional ion flotation is hydrodynamically constrained by coupling of the gas flux and liquid flux that report to the concentrate. This constraint has greatly limited the industrial application of ion flotation, despite its remarkable effectiveness in extracting ionic species down to very low concentrations, of order 1 ppm. Previous work demonstrated that these hydrodynamic constraints could be significantly relaxed using the reflux flotation cell (RFC), a system incorporating parallel inclined channels to improve bubble-liquid segregation. However, it was found that bubble coalescence placed an additional limit on performance. In this study the impact of coalescence was minimized by reducing the volume reduction from 20 to 5, ensuring sufficient liquid reported to the concentrate with the bubbles. Under these conditions, an equivalent adsorptive recovery was achieved using the RFC at feed fluxes up to four times those in the conventional system. The maximum adsorptive extraction rate achieved with the RFC was three times that for the conventional system. A refined experimental methodology was used to quantify much more accurately the relative hydrodynamic limits of conventional and RFC operation. The previously neglected issue of split-zone segregation, resulting in smaller bubbles in the lower part of the cell, was also investigated.

Comparison of Acoustic Streaming Flow Patterns Induced by Solid, Liquid and Gas Obstructions

In this study, acoustic streaming flows inside micro-channels induced by three different types of obstruction—gaseous bubble, liquid droplet and solid bulge—are compared and investigated experimentally by particle tracking velocimetry (PTV) and numerically using the finite element method (FEM). The micro-channels are made by poly(dimethylsiloxane) (PDMS) using soft lithography with low-cost micro-machined mold. The characteristic dimensions of the media are 0.2 mm in diameter, and the oscillation generated by piezoelectric actuators has frequency of 12 kHz and input voltages of 40 V. The experimental results show that in all three obstruction types, a pair of counter-rotating vortical patterns were observed around the semi-circular obstructions. The gaseous bubble creates the strongest vortical streaming flow, which can reach a maximum of 21 mm/s, and the largest u component happens at Y/D = 0. The solid case is the weakest of the three, which can only reach 2 mm/s. The liquid droplet has the largest v components and speed at Y/D = 0.5 and Y/D = 0.6. Because of the higher density and incompressibility of liquid droplet compared to the gaseous bubble, the liquid droplet obstruction transfers the oscillation of the piezo plate most efficiently, and the induced streaming flow region and average speed are both the largest of the three. An investigation using numerical simulation shows that the differing interfacial conditions between the varying types of obstruction boundaries to the fluid may be the key factor to these differences. These results suggest that it might be more energy-efficient to design an acoustofluidic device using a liquid droplet obstruction to induce the stronger streaming flow.